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The genus Amphora is one of the larger genera belonging to the family
Naviculaceae and includes about 350 taxa. It is a widespread genus
with a few species occurring in freshwater and brackish water, and
many species in marine habitats. Members of the genus are clearly
distinguished from related genera. The characteristic, strongly
dorsiventral frustule has raphe systems which lie close to the ventral
margins of the valve. There is no taxonomic revision and clear
definition of the genus Amphora based modern taxonomic criteria
covering both freshwater to marine species.

This study deal with the taxonomy the subgenus Amphora, for freshwater
and marine species in Japan. In addition to the characters observable
by light microscopy, characters revealed mainly by scanning and
transmission electron microscopy, such as raphe system and the shape
of dorsal marginal costa, were employed to establish the taxonomy of
the taxa considerd herein. Eighteen taxa are recognized in this
work. First, each taxon was observed in detail using SEM to expand
current knowledge of its fine structure. Taxonomic identification was
then confirmed with reference to type material or other historic
collections. Among the taxa investigated here, four are new to
science, one is a new combination and one is a new name. Ten of the
taxa investigated here (Amphora barrowiana (Patr. et Freese) Nagumo
comb. nov., A. copulata (Kützing) Schoeman et Archibald, A. hiromuii
Nagumo sp. nov., A. inariensis Krammer, A. liriope Nagumo sp. nov.,
A. macedoniensis Nagumo sp. nov., A. ovalis Kützing., A. pediculus
(Kützing) Grun., A. rotunda Skv., A. sibirica Skv. et Meyer) are from
freshwaters habitats. Three (A. arenicola (Grun.) Cleve, A. javanica
Schmidt, A. libyca Ehr.) are from brackish-water habitats and five
(A. gigantea Grun., A. immarginata Nagumo sp. nov., A. marina
W. Smith, A. plativalvata Nagumo nom. et stat. nov., A. schmidtii
Grun.) are from marine habitats.